Method of manufacturing heat spreader module

ABSTRACT

A heat spreader module has a pedestal, a heat spreader member joined to the pedestal by a first active hard brazing material, an intermediate layer joined to the heat spreader member by a second active hard brazing material, an insulating board joined to the intermediate layer by a third active hard brazing material, and a circuit board joined to the insulating board by a fourth active hard brazing material. The first through fourth active hard brazing materials are supplied such that the active hard brazing materials have a thickness ranging from 3 to 20 μm when the components of the heat spreader module are joined together under pressure, and contain an active element in an amount ranging from 400 to 1000 μg/cm 2 .

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 10/807,674,filed Mar. 24, 2004, and claims the benefit of Japanese Application2003-092511, filed Mar. 28, 2003, the entireties of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat spreader module for cooling anIC chip or the like which comprises semiconductors, etc.

2. Description of the Related Art

Generally, a heat spreader module for effectively dissipating the heatof a semiconductor device such as an IGBT (Insulated Gate BipolarTransistor) or the like comprises a circuit board, an insulating board,a heat spreader member (heat diffusion layer), and a pedestal. Ifnecessary, stress dampening layers may be disposed between thesecomponents of the heat spreader module. Heretofore, it has beencustomary to join these components with a solder layer (having a meltingpoint of about 250° C.).

However, the solder layers pose a large heat resistance, and themanufacturing cost for the heat spreader module is high because of twojoining processes required, i.e., a process of brazing the circuit boardand the insulating board to each other and a process of joining thejoined assembly to the pedestal.

The inventor of the present invention has disclosed, in Japaneselaid-open patent publication No. 2002-43482, a process of joining acircuit board, an insulating board, an intermediate layer, and a heatsink with an active hard brazing material under pressure and heat all inone sequence, leaving no joining layers which would pose a heatresistance. According to the disclosed process, a heat spreader modulehaving a high thermal conductivity can be manufactured inexpensively.

According to the above process of completing the joining of thecomponents in one sequence, if the active hard brazing material isexcessively supplied, then excess active hard brazing material issqueezed out around the pedestal when the components are joined. Theneed to remove the squeezed active hard brazing material results in anincrease in the manufacturing cost.

The melted hard brazing material that is squeezed out is brought intocontact with side edges of copper plates that are used as the circuitboard and the dampening layers. When the active hard brazing materialand the copper plates contact each other, they are alloyed, and thealloyed region has an electric conductivity and a thermal conductivitylower than those of copper, or has durability increased to make thestress dampening capability lower than that of copper, resulting in areduction in the quality of the heat spreader module.

One solution is to reduce the supplied amount of the active hard brazingmaterial for preventing excess active hard brazing material from beingsqueezed out around the pedestal. However, a reduction in the suppliedamount of the active hard brazing material tends to cause a shortage ofthe absolute amount of active elements required to join the components,giving rise to a new problem in that a necessary bonding strength cannotbe achieved.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a heatspreader module which does not produce excess active hard brazingmaterial and achieves a necessary bonding strength when components ofthe heat spreader module are joined, and a method of manufacturing sucha heat spreader module.

According to the present invention, there is provided a method ofmanufacturing a heat spreader module having a heat spreader member, aninsulating board, and a metal plate which are joined to a pedestal,comprising the steps of supplying active hard brazing materials eachcontaining an active element, between the pedestal, the heat spreadermember, the insulating board, and the metal plate, and pressing andheating the pedestal, the heat spreader member, the insulating board,and the metal plate to melt the active hard brazing materials, therebyjoining the pedestal, the heat spreader member, the insulating board,and the metal plate together, the active hard brazing materials beingsupplied such that the active hard brazing materials have a thicknessranging from 3 to 20 μm when the active hard brazing materials aremelted, the active element being contained in an amount ranging from 400to 1000 μg/cm².

Since the active hard brazing materials are supplied such that theirthickness is in the range from 3 to 20 μm at the time they are melted,when the pedestal, the heat spreader member, the intermediate layer, theinsulating board, and the metal plate are joined together under pressureand heat, any amount of the active hard brazing materials that issqueezed out is essentially eliminated or greatly reduced. Therefore,the step of removing any squeezed-out active hard brazing material maybe dispensed with, and the manufacturing cost of the heat spreadermodule may be lowered. Furthermore, alloying of the surface of the metalplate, squeezing-out of the active hard brazing materials onto a sideedge of a copper plate used as a buffer layer, and a reduction in astress dampening capability due to alloying are suppressed, preventingthe heat spreader module from being lowered in quality.

The active element is contained in an amount ranging from 50 to 2000μg/cm² or more preferably 426.8 to 1358 μg/cm². Therefore, the absoluteamount of the active element necessary to bond the components issufficiently obtained for a required bonding strength.

In the above manufacturing method, the active element should preferablybe Ti. Each of the active hard brazing materials should preferablycomprise a hard brazing material containing 3 to 15 weight % of Ti.Specifically, each of the active hard brazing materials shouldpreferably comprise an active hard brazing material of Ag—Cu—In—Ti.

In the above manufacturing method, each of the active hard brazingmaterials may be stacked as a plate or printed as a paste on a componentto be joined, or may be applied as a powder mixed with a binder to acomponent to be joined.

In the above manufacturing method, an active hard brazing materialpowder which comprises a mixture of a hard brazing material powder freeof an active element and an active element powder, or a paste producedfrom such an active hard brazing material powder may be used instead ofa hard brazing material containing an active element. The hard brazingmaterial free of an active element may comprise a hard brazing materialof Ag—Cu—In, and the active element may be Ti.

The heat spreader member should preferably be made of a compositematerial comprising a matrix of Carbon and/or Graphite Cu impregnatedwith Cu or Cu alloy or a composite material comprising a matrix of SiCimpregnated with Cu or Cu alloy.

The active hard brazing materials may be supplied between the pedestal,the heat spreader member, and the metal plate such that the active hardbrazing materials have a thickness ranging from 3 to 20 μm when theactive hard brazing materials are melted, and contain the active elementin an amount ranging from 426.8 to 1358 μg/cm², and wherein the activehard brazing material may be supplied between the insulating board andthe metal plate such that the active hard brazing material has athickness ranging from 3 to 20 μm when the active hard brazing materialis melted, and contains the active element in an amount ranging from 50to 1000 μg/cm².

According to the present invention, there is also provided a heatspreader module constructed by supplying active hard brazing materialseach containing an active element, between a pedestal, a heat spreadermember, an insulating board, and a metal plate, and pressing and heatingthe pedestal, the heat spreader member, the insulating board, and themetal plate to melt the active hard brazing materials, thereby joiningthe pedestal, the heat spreader member, the insulating board, and themetal plate together, the active hard brazing materials being suppliedsuch that the active hard brazing materials have a thickness rangingfrom 3 to 20 μm when the active hard brazing materials are melted, theactive element being contained in an amount ranging from 50 to 2000μg/cm², or preferably from 426.8 to 1358 μg/cm².

When the components of the heat spreader module are joined together, noexcess active hard brazing materials are produced, and the heat spreadermodule can have a necessary bonding strength.

According to the present invention, there is also provided a heatspreader module constructed by supplying active hard brazing materialseach containing an active element, between a pedestal, a heat spreadermember, an insulating board, and a metal plate, and pressing and heatingthe pedestal, the heat spreader member, the insulating board, and themetal plate to melt the active hard brazing materials, thereby joiningthe pedestal, the heat spreader member, the insulating board, and themetal plate together. The metal plate includes a marginal edge of alloyhaving a width within a range of 200 μm. The alloyed region of the metalplate includes constituent elements of the active hard brazingmaterials.

With the above arrangement, the insulating board and other componentsthat are positioned above and below the metal plate are prevented fromcracking. Therefore, the heat spreader module is highly reliable inoperation.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description withreference to the accompanying drawings which illustrate examples of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of a heat spreader moduleaccording to an embodiment of the present invention;

FIG. 2 is an enlarged fragmentary view showing an SiC/Cu compositematerial as an example of a heat spreader member;

FIG. 3 is an enlarged fragmentary view showing a C/Cu composite materialas another example of a heat spreader member;

FIG. 4A is a vertical cross-sectional view illustrative of a settingstep;

FIG. 4B is a vertical cross-sectional view illustrative of a joiningstep;

FIG. 5 is a vertical cross-sectional view illustrative of anotherjoining step;

FIG. 6 is a cross-sectional view of a sample used in first through thirdExperimental Examples;

FIG. 7A is a perspective view showing an appearance of ComparativeExample C1 after its components are joined under pressure;

FIG. 7B is a perspective view showing an appearance of ComparativeExample C2 after its components are joined under pressure;

FIG. 8A is a perspective view showing an appearance of Inventive ExampleE1 after its components are joined under pressure;

FIG. 8B is a perspective view showing an appearance of Inventive ExampleE2 after its components are joined under pressure;

FIG. 9A is a cross-sectional view showing an alloyed state of anintermediate layer in Comparative Example C1 after its components arejoined under pressure;

FIG. 9B is a cross-sectional view showing an alloyed state of anintermediate layer in Comparative Example C2 after its components arejoined under pressure;

FIG. 10A is a cross-sectional view showing an alloyed state of anintermediate layer in Inventive Example E1 after its components arejoined under pressure;

FIG. 10B is a cross-sectional view showing an alloyed state of anintermediate layer in Inventive Example E2 after its components arejoined under pressure;

FIG. 11 is a diagram showing different squeezed amounts of active hardbrazing materials with respect to different thicknesses of the activehard brazing materials when they are supplied, as measured in a thirdExperimental Example;

FIG. 12 is a cross-sectional view of a sample used in fourth throughsixth Experimental Examples;

FIG. 13 is a diagram showing different bonding strengths of heatspreader modules with respect to different amounts of Ti contained inactive hard brazing materials, as measured in the fourth ExperimentalExample;

FIG. 14 is a cross-sectional view of a sample used in the fifthExperimental Example;

FIG. 15 is a diagram showing different bonding strengths with respect todifferent amounts of Ti between an insulating board of SN and a circuitboard of Cu and also between an insulating board of SN and anintermediate layer, as measured in the fifth Experimental Example;

FIG. 16 is a diagram showing different thermal conductivities of heatspreader modules with respect to different amounts of Ti contained inactive hard brazing materials, as measured in the sixth ExperimentalExample; and

FIG. 17 is a diagram showing bonding strengths, thermal conductivities,squeezed amounts of active hard brazing materials, and alloyed states ofintermediate layers of samples 1 through 23, as measured in a seventhExperimental Example.

DETAILED DESCRIPTION OF THE INVENTION

A heat spreader module and a method of manufacturing such a heatspreader module will be described below with reference to FIGS. 1through 17.

As shown in FIG. 1, a heat spreader module according to an embodiment ofthe present invention comprises a pedestal 12, a heat spreader member 14disposed above the pedestal 12, a thermally conductive layer 16 disposedon the heat spreader member 14, a first active hard brazing material 18interposed between the pedestal 12 and the heat spreader member 14, anda second active hard brazing material 20 interposed between the heatspreader member 14 and the thermally conductive layer 16.

The thermally conductive layer 16 comprises an insulating board 22, anintermediate layer 24 interposed between the insulating board 22 and theheat spreader member 14, a circuit board 26 of Cu or Al disposed abovethe insulating board 22, a third active hard brazing material 28interposed between the intermediate layer 24 and the insulating board22, and a fourth active hard brazing material 30 interposed between theinsulating board 22 and the circuit board 26.

An IC chip 34 is mounted on a base layer 32 disposed on the circuitboard 26. A heat sink 36 made of Al or Cu as a heat radiator is securedby screws (not shown), for example, to the lower surface of the pedestal12. The insulating board 22 may be made of AlN or Si₃N₄.

The order in which the components of the heat spreader module arepositioned, i.e., the order of the pedestal 12, the heat spreader member14, the insulating board 22, the intermediate layer 24, and the circuitboard 26, is not limited to the order shown in FIG. 1. Insofar as thepedestal 12 is positioned adjacent to the heat sink 36 and the circuitboard 26 is positioned adjacent to the IC chip 34 with the base layer 32interposed therebetween, each of the intermediate layer 24 and the heatspreader member 14 may not be a single layer, but may be a combinationof layers, and the insulating board 22 may not be disposed directlybelow the circuit board 26, but may be disposed in any suitable positionanywhere between the pedestal 12 and the circuit board 26.

The thermal conductivity of the heat spreader member 14 shouldpreferably be 150 W/mK or higher. If the thermal conductivity of theheat spreader member 14 is lower than 150 W/mK, then the heat generatedby the IC chip 34 during operation of the heat spreader module 10 istransferred out of the heat spreader module 10 at a lower speed,resulting in a poorer ability to keep the heat spreader module 10 at aconstant temperature.

The heat spreader member 14 is made of any material or materials as longas its thermal conductivity or coefficient of thermal expansion falls inthe above range. Preferably, the heat spreader member 14 should be madeof at least one material selected from the group consisting of SiC, AlN,Si₃N₄, BeO, Al₂O₃, Be₂C, C, Cu, Cu alloy, Al, Al alloy, Ag, Ag alloy,and Si. That is, the heat spreader member 14 may be made of a singlematerial selected from the above group or a composite materialcomprising at least two materials selected from the above group. Forexample, such a composite material may be a SiC/Cu composite material 40(see FIG. 2) or a C/Cu composite material 42 (see FIG. 3).

As shown in FIG. 2, the SiC/Cu composite material 40 comprises a poroussintered body 44 of Sic having open pores 46 impregnated with melted Cuor Cu alloy 48, which is subsequently solidified.

As shown in FIG. 3, the C/Cu composite material 42 comprises a poroussintered body 50 which is produced by preliminarily sintering carbon oran isotope thereof into a network, the porous sintered body 50 havingopen pores 52 impregnated with melted Cu or Cu alloy 54, which issubsequently solidified. The C/Cu composite material 42 is disclosed inJapanese laid-open patent publication No. 2001-339022, for example.

If the heat spreader member 14 is made of any of composite materials oralloys referred to above, the coefficient of thermal expansion and thethermal conductivity thereof can be controlled at a range from 3.0×10⁻⁶to 1.0×10⁻⁵/K and at least 150 W/mK, respectively, by setting acomposition ratio of the constituents.

The first through fourth active hard brazing materials 18, 20, 28, 30should preferably be an active hard brazing material containing anactive element or elements. The active element or elements may be atleast one of elements belonging to the periodic table, group 2A (IIA,2), such as Mg, Sr, Ca, Ba, Be, etc., group 3A (IIIB, 3), such as Ce,etc., group 4A (IVB, 4), such as Ti, Zr, etc., group 5A (VB, 5), such asNb, etc., group 3B (IIIA, 13), such as B, etc., or group 4B (IVA, 14),such as Si, etc. In the present embodiment, the first through fourthactive hard brazing materials 18, 20, 28, 30 comprise a hard brazingmaterial of Ag—Cu—In—Ti where Ti is an active element.

As shown in FIG. 1, the base layer 32 comprises a solder layer 60disposed on the thermally conductive layer 16 and an Ni layer 62disposed on the solder layer 60 for increasing the wettability of the ICchip 34 with respect to the solder layer 60. The pedestal 12 is made ofpure copper or copper alloy.

A process of manufacturing the heat spreader module 10 according to thepresent embodiment will be described below with reference to FIGS. 4Athrough 5.

FIG. 4A illustrates a setting step. In the setting step, the firstactive hard brazing material 18 in the form of a plate, the heatspreader member 14, the second active hard brazing material 20 in theform of a plate, the intermediate layer 24, the third active hardbrazing material 28 in the form of a plate, the insulating board 22, thefourth active hard brazing material 30 in the form of a plate, and thecircuit board 26 are placed on the pedestal 12 successively in the ordernamed. The setting step is performed in the atmosphere, for example.

FIG. 4B illustrates a joining step. In the joining step, the pedestal12, on which the first active hard brazing material 18, the heatspreader member 14, the second active hard brazing material 20, theintermediate layer 24, the third active hard brazing material 28, theinsulating board 22, the fourth active hard brazing material 30, and thecircuit board 26 are set, is fixedly mounted on a jig 70. The assemblyis placed in a vacuum of 1.0×10⁻⁵ Torr or lower, and is pressed fromabove to join the components together while the temperature is beingraised and lowered. The joining step thus performed produces anintegrally joined assembly of the circuit board 26, the insulating board22, the intermediate layer 24, the heat spreader member 14, and thepedestal 12, i.e., the heat spreader module 10, as shown in FIG. 1.

In FIG. 4A, the first through fourth active hard brazing materials 18,20, 28, 30 each in the form of a plate are employed. However, as shownin FIG. 5, the first through fourth active hard brazing materials 18,20, 28, 30 may be employed each in the form of a paste. Specifically,the heat spreader member 14 that is coated with the second active hardbrazing material 20 is placed on the pedestal 12 that is coated with thefirst active hard brazing material 18, and the intermediate layer 24that is coated with the third active hard brazing material 28 is placedon the heat spreader member 14.

Then, the insulating board 22 that is coated with the fourth active hardbrazing material 30 is placed on the intermediate layer 24, and thecircuit board 26 is placed on the insulating board 22. The setting stepwherein the first through fourth active hard brazing materials 18, 20,28, 30 each in the form of a paste are applied is now completed.

In the joining step shown in FIG. 4B, the assembly should preferably bepressed under a pressure in the range from 0.2 MPa to 10 MPa.

According to the present embodiment, in the setting step shown in FIG.4A or 5, the first through fourth active hard brazing materials 18, 20,28, 30 are supplied in such quantities that when they are melted underpressure and heat so as to be joined together, they have an averagethickness in the range from 3 to 20 μm.

The amount of Ti contained in each of the first through fourth activehard brazing materials 18, 20, 28, 30 should preferably be in the rangefrom 50 to 2000 μg/cm² or more preferably be in the range from 426.8 to1358 μg/cm².

Since the first through fourth active hard brazing materials 18, 20, 28,30 are supplied such that their average thickness is in the range from 3to 20 μm at the time they are melted under pressure and heat so as to bejoined together, when the pedestal 12, the heat spreader member 14, theintermediate layer 24, the insulating board 22, and the circuit board 26are joined together under pressure, any amount of active hard brazingmaterial 80 (see FIG. 7A, for example) that is squeezed out isessentially eliminated or greatly reduced. Therefore, the step ofremoving the squeezed-out active hard brazing material 80 may bedispensed with, and the manufacturing cost of the heat spreader module10 may be lowered. In addition, alloying of the surface of theintermediate layer 24 which is in the form of a metal plate issuppressed, so that the quality of the heat spreader module 10 will notbe reduced. The circuit board 26 is often in the form of a thin platehaving a thickness ranging from 0.1 to 0.3 mm. Therefore, anysqueezed-out active hard brazing material 80 that is applied to the sideedges of the circuit board 26 is extremely small, and hence the activehard brazing material 80 and the circuit board 26 are essentially notalloyed.

The bonding strength between the components depends on the amount of Ticontained in each of the first through fourth active hard brazingmaterials 18, 20, 28, 30. In the present embodiment, inasmuch as theamount of Ti contained in each of the first through fourth active hardbrazing materials 18, 20, 28, 30 is preferably in the range from 50 to2000 μg/cm² or more preferably in the range from 426.8 to 1358 μg/cm²,the absolute amount of Ti necessary to bond the components issufficiently obtained for a required bonding strength.

Seven Experimental Examples will be described below. In the firstExperimental Example, squeezed-out states of the active hard brazingmaterial 80 are observed for appearance with respect to several samples(Comparative Examples C1, C2 and Inventive Examples E1, E2). As shown inFIG. 6, these samples have such a common structure that two joinedassemblies 82, 84 are stacked with a buffer layer 86 interposedtherebetween. Each of the joined assemblies 82, 84 is constructed of theheat spreader member 14 (having a thickness of 3.0 mm) made of the C/Cucomposite material 42 (see FIG. 3), the second active hard brazingmaterial 20 placed on the heat spreader member 14, the intermediatelayer 24 (having a thickness of 0.25 mm) made of Cu which is placed onthe second active hard brazing material 20, the third active hardbrazing material 28 placed on the intermediate layer 24, the insulatingboard 22 (having a thickness of 0.3 mm) of SN which is placed on thethird active hard brazing material 28, the fourth active hard brazingmaterial 30 placed on the insulating board 22, and the circuit board 26(having a thickness of 0.3 mm) of Cu which is placed on the fourthactive hard brazing material 30.

The samples were placed in a vacuum of 1.0×10⁻⁵ Torr or lower at atemperature of 830° C., and were pressed under a pressure of 3.5 MPa tojoin the components together. The samples were pressed for 10 minutes.

In Comparative Example C1, each of the second through fourth active hardbrazing materials 20, 28, 30 had a thickness of 50 μm at the time thecomponents were joined under pressure. In Comparative Example C2, eachof the second through fourth active hard brazing materials 20, 28, 30had a thickness of 30 μm at the time the components were joined underpressure. In Inventive Example E1, each of the second through fourthactive hard brazing materials 20, 28, 30 had a thickness of 20 μm at thetime the components were joined under pressure. In Inventive Example E2,each of the second through fourth active hard brazing materials 20, 28,30 had a thickness of 10 μm at the time the components were joined underpressure.

The appearances of the samples after the experimentation are shown inFIGS. 7A through 8B. In Comparative Example C1, as shown in FIG. 7A, itcan be seen a large amount of excess active hard brazing material 80 wassqueezed out when the components were pressed, with a large amount ofactive hard brazing material 80 applied to the side edges of the circuitboard 26 and the intermediate layer 24. In Comparative Example C2, asshown in FIG. 7B, it can be seen some excess active hard brazingmaterial 80 was squeezed out when the components were pressed, withactive hard brazing material 80 applied to the side edges of the circuitboard 26 and the intermediate layer 24.

In Inventive Example E1, as shown in FIG. 8A, the amount of excessactive hard brazing material 80 that was squeezed out when thecomponents were pressed is small, with almost no active hard brazingmaterial 80 applied to the side edges of the circuit board 26 and theintermediate layer 24. In Inventive Example E2, as shown in FIG. 8B, noactive hard brazing material 80 was squeezed out when the componentswere pressed is small, with no active hard brazing material 80 appliedto the side edges of the circuit board 26 and the intermediate layer 24.

In the second Experimental Example, Comparative Examples C1, C2 andInventive Examples E1, E2 that were experimented were broken vertically,and the intermediate layers 24 were observed about how they were alloyedand the insulating boards 22 were observed about how they cracked. Theexperimental results are shown in FIGS. 9A through 10B.

In Comparative Example C1, as shown in FIG. 9A, the intermediate layer24 was alloyed by a depth of about 200 μm from its side edge toward thecenter thereof (see an alloyed range a1). In Comparative Example C2, asshown in FIG. 9B, the intermediate layer 24 was alloyed by a depth ofabout 100 μm from its side edge toward the center thereof (see analloyed range a2). In Comparative Example C1, since the alloyed rangewas large, the insulating board 22 had cracks 90 therein.

In Inventive Example E1, as shown in FIG. 10A, the intermediate layer 24was alloyed by a depth of about 20 μm from its side edge toward thecenter thereof (see an alloyed range b1). The alloyed range b1 is muchsmaller than those in Comparative Examples C1, C2. In Inventive ExampleE2, as shown in FIG. 10B, the intermediate layer 24 was alloyed by adepth of about 10 μm from its side edge toward the center thereof (seean alloyed range b2). It will be understood that the intermediate layer24 in Inventive Example E2 was almost not alloyed.

In the third Experimental Example, the samples (see FIG. 6) which arethe same as those in the first Experimental Example were measured fordifferent amounts of squeezed-out active hard brazing material 80 withrespect to different thicknesses of the second through fourth activehard brazing materials 20, 28, 30 at the time they were supplied. Thedifferent amounts of squeezed-out active hard brazing material 80 weremeasured by cutting off the squeezed-out active hard brazing material 80and measuring the weight thereof.

The measured results are shown in FIG. 11. In FIG. 11, plots indicatedby ⋄ (:Empty Diamond) represent amounts of squeezed-out active hardbrazing material 80 when a active hard brazing material containing 2.2weight % of Ti was used as the second through fourth active hard brazingmaterials 20, 28, 30, and plots indicated by ▪ (:Filled Square)represent amounts of squeezed-out active hard brazing material 80 whenan active hard brazing material containing 7 weight % of Ti was used asthe second through fourth active hard brazing materials 20, 28, 30. Astraight-line curve G which is inclined upwardly to the right representschanges in the total weight of the second through fourth active hardbrazing materials 20, 28, 30 when they were supplied.

As shown in FIG. 11, the amount of squeezed-out active hard brazingmaterial 80 increases as the thicknesses of the supplied second throughfourth active hard brazing materials 20, 28, 30 increase. It can also beseen that the difference between the amount of squeezed-out active hardbrazing material 80 and the total weight of the second through fourthactive hard brazing materials 20, 28, 30 when they were supplied, i.e.,the amount of active hard brazing material 80 that contributed to thejoining of the components, remains substantially unchanged.

Consequently, it can be understood from the third Experimental Examplethat since the weight of active hard brazing material 80 thatcontributed to the joining of the components remains substantiallyunchanged, it is useless to supply an amount of active hard brazingmaterial in excess of that weight, and if an amount of active hardbrazing material in excess of that weight is supplied, then theintermediate layer 24 will undesirably be alloyed, resulting incharacteristic degradations.

The fourth Experimental Example will be described below. In the fourthExperimental Example, different bonding strengths of the heat spreadermodule with respect to the amounts of Ti contained in the second throughfourth active hard brazing materials 20, 28, 30 were observed.

In the fourth Experimental Example, there were prepared samples wherein59.8Ag—24Cu—14In—2.2Ti (“2.2Ti material”) was employed as the firstthrough fourth active hard brazing materials 18, 20, 28, 30 and thesamples had respective thicknesses of 5 μm, 7.5 μm, 10 μm, 15 μm, and 20μm when they were supplied, and samples wherein 58Ag—22Cu—13In—7Ti (“7Timaterial”) was employed as the first through fourth active hard brazingmaterials 18, 20, 28, 30 and the samples had respective thicknesses of 5μm, 7.5 μm, 10 μm, 15 μm, and 20 μm when they were supplied.

As shown in FIG. 12, each of the samples of the 2.2Ti material and the7Ti material is constructed of the first active hard brazing material 18that is placed on the pedestal 12 (having a thickness of 2.0 mm) made ofCu, the heat spreader member 14 (having a thickness of 3.0 mm) made ofthe C/Cu composite material which is placed on the first active hardbrazing material 18, the second active hard brazing material 20 placedon the heat spreader member 14, the intermediate layer 24 (having athickness of 1.0 mm) placed on the second active hard brazing material20, the third active hard brazing material 28 placed on the intermediatelayer 24, the insulating board 22 (having a thickness of 0.3 mm) of SNwhich is placed on the third active hard brazing material 28, the fourthactive hard brazing material 30 placed on the insulating board 22, andthe circuit board 26 (having a thickness of 0.2 mm) of Cu which isplaced on the fourth active hard brazing material 30.

The samples of the 2.2Ti material and the 7Ti material were subjected toa peel test in which terminals were joined to the pedestal 12 and thecircuit board 26 and the samples were simply pulled vertically. In thepeel test, the samples were measured for a strength at the time thejoined surfaces (active hard brazing material surfaces) were peeled offor a strength at the time the heat spreader member 14 was fractured. Ifthe joined surfaces are peeled off, then it means that the bondingstrength is too low, and if the heat spreader member 14 is fractured,then it means that the bonding strength is high and the joined surfacesare highly reliable.

The measured results of the fourth Experimental Example are shown inFIG. 13. In FIG. 13, the horizontal axis represents graduations for thethicknesses of the active hard brazing materials 18, 20, 28, 30 of thesamples of the 2.2Ti material, graduations for the thicknesses of theactive hard brazing materials 18, 20, 28, 30 of the samples of the 7Timaterial, and graduations for amounts of contained Ti.

In FIG. 13, plots indicated by □ (:Empty Square) represent strengths atthe time the joined surfaces of the samples of the 2.2Ti material werepeeled off, and plots indicated by ▪ (:Filled Square) representstrengths at the time the heat spreader member 14 of the samples of the2.2Ti material were fractured. Similarly, plots indicated by 0∘ (:EmptyCircle) represent strengths at the time the joined surfaces of thesamples of the 7Ti material were peeled off, and plots indicated by (:Filled Circle) represent strengths at the time the heat spreadermember 14 of the samples of the 7Ti material were fractured. The peelingoff of each of the joined surfaces took place at the interface betweenthe heat spreader member 14 and the pedestal 12 or the interface betweenthe heat spreader member 14 and the intermediate layer 24.

It can be seen from the experimental results shown in FIG. 13 that withrespect to the samples of the 2.2Ti material, the joined surfaces werepeeled off in all the thicknesses ranging from 5 to 20 μm, and the heatspreader member 14 was also fractured in the sample having the thicknessof 20 μm.

It can also be seen that with respect to the samples of the 7Timaterial, the joined surfaces were peeled off in the sample having thethickness of 5 μm, and that sample had a bonding strength of 20 MPawhich is of a practical level, and the heat spreader member 14 wasfractured, but the joined surfaces were not peeled off, in all thesamples having the thicknesses ranging from 7.5 to 20 μm.

Of the samples of the 2.2Ti material, the sample having the thickness of20 μm contained about 420 μg/cm² of Ti. Of the samples of the 7Timaterial, the sample having the thickness of 5 μm contained about 350μg/cm² of Ti. It can thus be seen that if the amount of contained Tirequired to join the heat spreader member 14 and the pedestal 12 to eachother and also to join the heat spreader member 14 and the intermediatelayer 24 is 400 μg/cm² or greater, then the bonding strength that isachieved is of a practical level.

The fifth Experimental Example will be described below. The fifthExperimental Example employed samples of 60Ag—24.7Cu—14In—1.3Ti (“1.3Timaterial”) and samples of the 2.2Ti material. Each of the samples of thethird and fourth types is constructed of, as shown in FIG. 14, the firstactive hard brazing material 18 that is placed on the intermediate layer24 (having a thickness of 1.0 mm) made of Cu, the insulating board 22(having a thickness of 0.3 mm) of SN which is placed on the first activehard brazing material 18, the fourth active hard brazing material 30that is placed on the insulating board 22, and the circuit board 26(having a thickness of 0.2 mm) of Cu which is placed on the secondactive hard brazing material 20.

In the fifth Experimental Example, the samples were observed fordifferent bonding strengths with respect to different amounts of Tirequired to join the insulating board 22 of SN and the circuit board 26of Cu to each other and also to join the insulating board 22 of SN andthe intermediate layer 24 to each other.

The measured results are shown in FIG. 15. In the fifth ExperimentalExample, the samples of the first and second types were subjected to apeel test in which terminals were joined to the intermediate layer 24and the circuit board 26 and the samples were simply pulled vertically.Those samples which had joined surfaces peeled off were judged as beingrejected (NG), and those samples which had the insulating board 22itself fractured were judged as being acceptable (OK) because thebonding strength was regarded as being of a practical level.

It can be seen from the results shown in FIG. 15 that with respect tothe samples of the 1.3Ti material, the joined surfaces were peeled offin the sample having the thickness of 3 μm, and the insulating board 22was fractured in those samples having the thicknesses ranging from 5 to20 μm.

It can also be seen from the results shown in FIG. 15 that with respectto the samples of the 2.2Ti material, the insulating board 22 wasfractured in all those samples having the thicknesses ranging from 3 to20 μm.

Of the samples of the 1.3Ti material, the sample having the thickness of3 μm contained about 38 μg/cm² of Ti, and the sample having thethickness of 5 μm contained about 63 μg/cm² of Ti. It can thus be seenthat if the amount of contained Ti required to join the insulating board22 of SN and the circuit board 26 of Cu to each other and also to jointhe insulating board 22 of SN and the intermediate layer 24 to eachother is 50 μg/cm² or greater, then the bonding strength that isachieved is of a practical level.

The sixth Experimental Example will be described below. In the sixthExperimental Example, different thermal conductivities of heat spreadermodules 10 with respect to different amounts of Ti contained in thefirst through fourth active hard brazing materials 18, 20, 28, 30 wereobserved. Specifically, the samples of the 2.2Ti material and the 7Timaterial in the fourth Experimental Example were measured for thermalconductivities.

The measured results are illustrated in FIG. 16. In FIG. 16, plotsindicated by □ (:Empty Square) represent thermal conductivities of thesamples of the 2.2Ti material, and plots indicated by  (:Filled Circle)represent thermal conductivities of the samples of the 7Ti material.

All the samples of the 2.2Ti material, and those samples of the 7Timaterial in which the first through fourth active hard brazing materials18, 20, 28, 30 had respective thicknesses of 5 μm, 7.5 μm, 10 μm, and 15μm when they were supplied had thermal conductivities of 350 W/mK orhigher. However, those samples of the 7Ti material in which the firstthrough fourth active hard brazing materials 18, 20, 28, 30 hadrespective thicknesses of 20 μm (which can be converted into 1300 μg/cm²as the amount of contained Ti) when they were supplied had thermalconductivities less than 350 W/mK.

It can be understood from FIG. 16 that if the amount of contained Ti is1200 μg/cm² or less, then the thermal conductivity that is achieved isof a practical level.

The seventh Experimental Example will be described below. The seventhExperimental Example serves as a general experiment, and was conductedto observe bonding strengths, thermal conductivities, squeezed amountsof active hard brazing material 80, and alloyed states of theintermediate layer 24 of samples 1 through 23 (having the samestructural details as shown in FIG. 12) that were joined under thejoining conditions described below.

Alloyed states were judged as “x” if the applied amount of brazingmaterial was in excess of 20 μm and the intermediate layer 24 wasalloyed by a depth of 200 μm or greater from its side edge toward thecenter thereof, “◯” if the applied amount of brazing material was in therange from 10 to 20 μm and the intermediate layer 24 was free of analloyed region beyond the depth of 200 μm, and “⊙” if the applied amountof brazing material was less than 10 μm and the intermediate layer 24was alloyed by a depth of 100 μm or smaller.

The samples were joined under a pressure of 3.5 MPa in a vacuum of1.0×10⁻⁵ Torr or lower at a temperature of 830° C. for 10 minutes.

The bonding strength was judged by pulling the samples 1 through 23 anddetermining whether the joined interfaces were peeled off (NG) or notand whether the heat spreader member 14 was fractured (OK) or not.

The squeezed amount of active hard brazing material 80 was measured asfollows: Attention was directed to the circuit board 26 which issubstantially not alloyed by an active hard brazing material that hasbeen squeezed out, and the amount of active hard brazing material 80squeezed out from between the circuit board 26 and the insulating board22 positioned therebeneath was measured, after which the measured amountwas multiplied by 4.

The details of the samples 1 through 23 (the compositions of the firstthrough fourth active hard brazing materials 18, 20, 28, 30, thesupplied amounts of the first through fourth active hard brazingmaterials 18, 20, 28, 30, and the amounts of contained Ti) and themeasured results are shown in FIG. 17. In FIG. 17, W1 represents thesupplied amounts of the first through fourth active hard brazingmaterials 18, 20, 28, 30, W2 represents the amounts of contained Ti, λmrepresents the thermal conductivities of the heat spreader modules 10,and hm represents the squeezed amounts of the first through fourthactive hard brazing materials 18, 20, 28, 30.

With respect to the compositions of the first through fourth active hardbrazing materials 18, 20, 28, 30 in the description which follows, thosematerials having a composition of 60Ag—24.7Cu—14In—1.3Ti are referred toas “1.3Ti material”, those materials having a composition of59.8Ag—24Cu—14In—2.2Ti as “2.2Ti material”, those materials having acomposition of 58.4Ag—23.5Cu—13.5In—4.5Ti as “4.5Ti material”, and thosematerials having a composition of 58Ag—22Cu—13In—7Ti as “7Ti material”.

First, the bonding strength in the measured results shown in FIG. 17will be described below. Of the samples 1 through 4 which employed the1.3Ti material, the samples 1 through 3 are judged as “NG”, and acritical point of the amount of contained Ti for judging the samples 1through 3 as “NG” exists between 378.3 μg/cm² of the sample 3 and 630.5μg/cm² of the sample 4.

Of the samples 5 through 11 which employed the 2.2Ti material, thesamples 5 through 7 are judged as “NG”, and a critical point of theamount of contained Ti for judging the samples 5 through 7 as “NG”exists between 213.4 μg/cm² of the sample 7 and 320.1 μg/cm² of thesample 8.

Of the samples 12 through 17 which employed the 4.5Ti material, thesample 12 is judged as “NG”, and a critical point of the amount ofcontained Ti for judging the sample 12 as “NG” exists between 218.25μg/cm² of the sample 12 and 327.6 μg/cm² of the sample 13.

Of the samples 18 through 23 which employed the 7Ti material, no sampleis judged as “NG”, and a critical point of the amount of contained Tifor judging samples as “NG” exists below 339.5 μg/cm².

Those samples which had thermal conductivities less than 350 W/mKinclude the sample 11 (whose Ti content was 1067 μg/cm², the sample 16(whose Ti content was 873 μg/cm², the sample 17 (whose Ti content was1309.5 μg/cm², the sample 21 (whose Ti content was 1018.5 μg/cm², thesample 22 (whose Ti content was 1358 μg/cm², and the sample 23 (whose Ticontent was 2037 μg/cm²).

Therefore, a critical point for determining the thermal conductivity of350 W/mK exists between 873 μg/cm² of the sample 16 and 1067 μg/cm² ofthe sample 11.

The alloyed state of the intermediate layer 24 was judged as “x” in thesamples 3, 10, 17, 23 where the first through fourth active hard brazingmaterials 18, 20, 28, 30 were supplied in an amount of 29.1 mg/cm², andthe samples 4, 11 where the first through fourth active hard brazingmaterials 18, 20, 28, 30 were supplied in an amount of 48.5 mg/cm².

The supplied amount of 29.1 mg/cm² for the active hard brazing materials18, 20, 28, 30 may be converted into a thickness of 30 μm at the timethey are supplied, and the supplied amount of 48.5 mg/cm² for the activehard brazing materials 18, 20, 28, 30 may be converted into a thicknessof 50 μm at the time they are supplied.

It can be seen from the results of the seventh Experimental Example thatif the thickness of the active hard brazing materials 18, 20, 28, 30when they are supplied is less than 20 μm and the amount of contained Tiis in the range from 426.8 to 1358 μg/cm², then it is possible for theheat spreader module 10 to have a thermal conductivity of 350 W/mK orhigher and a sufficient bonding strength, and to be essential free ofalloying in the intermediate layer 24.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

1. A method of manufacturing a heat spreader module having a heatspreader member, an insulating board, and a metal plate which are joinedto a pedestal, comprising the steps of: supplying active hard brazingmaterials each containing an active element, between said pedestal, saidheat spreader member, said insulating board, and said metal plate; andpressing and heating said pedestal, said heat spreader member, saidinsulating board, and said metal plate to melt said active hard brazingmaterials, thereby joining said pedestal, said heat spreader member,said insulating board, and said metal plate together; said active hardbrazing materials being supplied such that said active hard brazingmaterials have a thickness ranging from 3 to 20 μm when said active hardbrazing materials are melted, said active element being contained in anamount ranging from 400 to 1000 μg/cm².
 2. A method according to claim1, wherein each of said active hard brazing materials comprises amixture of said active element and a hard brazing material.
 3. A methodaccording to claim 1, wherein said active element comprises Ti.
 4. Amethod according to claim 3, wherein each of said active hard brazingmaterials comprises a hard brazing material containing 3 to 15 weight %of Ti as the active element or a hard brazing material mixed with 3 to15 weight % of Ti as the active element.
 5. A method according to claim3, wherein each of said active hard brazing materials comprises anactive hard brazing material of Ag—Cu—In—Ti or a mixture of a hardbrazing material of Ag—Cu—In and an active element Ti.
 6. A methodaccording to claim 1, wherein said heat spreader member is made of acomposite material comprising a matrix of Carbon and/or Graphiteimpregnated with Cu or Cu alloy, or a composite material comprising amatrix of SiC impregnated with Cu or Cu alloy.
 7. A method according toclaim 6, wherein said hard brazing materials are supplied between saidpedestal, said heat spreader member, and said metal plate such that saidactive hard brazing materials have a thickness ranging from 3 to 20 μmwhen said active hard brazing materials are melted, and contain saidactive element in an amount ranging from 400 to 1000 μg/cm², and whereinsaid active hard brazing material is supplied between said insulatingboard and said metal plate such that said active hard brazing materialhas a thickness ranging from 3 to 20 μm when said active hard brazingmaterial is melted, and contains said active element in an amountranging from 50 to 1000 μg/cm².